High-Side Current Detection Circuit for Accurate Output Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-side switching circuits face challenges in accurately detecting currents due to variations in on-resistance and temperature dependencies of transistors, leading to inaccurate detection of output currents.
Innovation Solution
A current detecting circuit with a series configuration of switching circuits and a current amplifier that detects the difference between output voltages, using transistors with specific resistance ratios to enhance accuracy and prevent backflow, while scaling down transistor sizes to reduce chip area and eliminate the need for external converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transistors are used for high-side switching, then switching function is achieved, but on-resistance variations and temperature dependencies cause inaccurate current detection
Solution Approach 1:
The patent creates a copy of the transistor circuit (first switching circuit M1-M2) and uses it to generate a reference current that mirrors the output current. By copying the transistor characteristics and using differential measurement between the original and copied circuits, the system eliminates errors caused by transistor on-resistance variations and temperature dependencies.
Solution Approach 2:
The patent introduces an intermediary current mirror circuit and differential amplifier that mediates between the transistor switching operation and the current detection. This intermediary structure converts the difficult-to-measure transistor on-resistance variations into a measurable voltage difference while blocking the harmful effects of temperature dependencies.
2Object-affected harmful factors
If parasitic diodes are used to prevent backflow, then backflow protection is achieved, but detection accuracy is reduced due to short-circuiting effects
Solution Approach 1:
The patent segments the backflow protection function from the current detection function. Instead of relying on parasitic diodes that affect the entire circuit, it uses dedicated third and fourth switching circuits (M3-M4) specifically for backflow protection, while the first and second switching circuits (M1-M2) handle current detection independently.
Solution Approach 2:
The patent uses a copy of the switching circuit structure (third and fourth switching circuits) to provide backflow protection without interfering with the detection circuit. The copied structure mirrors the functionality of the first switching circuit while being electrically isolated for protection purposes only.
3Measurement precision
If multiple switching circuits and current amplifier are added to improve detection accuracy, then detection precision is improved, but chip area increases
Solution Approach 1:
The patent implements a nested structure where the current mirror circuits are embedded within the switching circuit framework. The third and fourth switching circuits are nested as parallel copies of the first switching circuit, sharing common control signals and power supply connections, thereby reducing redundant components and minimizing chip area.
Solution Approach 2:
The patent designs the switching circuits to serve multiple functions: the first switching circuit performs both switching and current detection, while the third switching circuit provides both switching and backflow protection. This multi-functionality reduces the total number of components needed and decreases chip area.
Data Source
AI summary
A current detecting circuit includes a first switching element, a second switching element, and a third switching element electrically coupled in series with the first switching element. An output side of the third switching element is electrically coupled to an output terminal. The current detecting circuit includes a current amplifier configured to detect a difference between a first output voltage of the first switching element and a second output voltage of the second switching element. The current amplifier outputs a relative current to be used for detecting an output current that flows out from the output terminal. A ratio of resistance associated with the first switching element to resistance associated with the second switching element is n:1.